OAHN Small Ruminant Network Project: Investigation of Pooling Serum Samples for Maedi Visna Testing

Project Lead: Dr. Rex Crawford

Collaborators:  Dr. Jocelyn Jansen, Dr. Cathy Bauman

To download a copy of the full project report, please click here: https://www.oahn.ca/wp-content/uploads/2023/12/OAHN-Small-Ruminant-Project-pooling-serum-samples-for-maedi-visna-testing.pdf

The Ontario Maedi Visna Flock Status Program (OMVFSP) administered by Ontario Sheep Farmers recently completed an update to their protocols.  As part of that review, feedback was solicited from producers enrolled in the program.  One of the primary concerns of producers was the cost to complete whole flock individual animal testing – both in small and large flocks.  The participating producers encouraged the Technical Committee to allow individual serum samples to be pooled prior to testing with the Hyphen Elitest ELISA.

Québec has a maedi visna (mv) flock status program similar to the OMVFSP, where pooling has been allowed for a number of years, using the Hyphen Elitest ELISA.  The Québec program allows 5 samples to be pooled and uses a cut-point Optical Density of 0.100.  Their validation study with 10 “high positive” and 25 “low positive” samples diluted with 4 previously negative samples indicated a loss of approximately 20% sensitivity (Simon Tremblay, personal communication).  In 2021 they found approximately 17% of pools positive – with approximately 70% of those pools having at least 1 individual positive sample when retested individually.

The objective of this study was to: 1) determine cut-points for both pools of 3 samples and pools of 5 samples using the Hyphen Elitest ELISA at the Animal Health Laboratory, University of Guelph (AHL) and 2) evaluate the sensitivity and specificity of those cut-points so that the technical committee could make an informed decision regarding the use of pooling in the OMVFSP.